Endoscopic surgery is becoming increasingly popular because of the following reasons:    (a) it is a minimally invasive form of surgery,    (b) it avoids large incisions over the skin and muscle,    (c) it is associated with less pain,    (d) there is a relatively less requirement of blood transfusions and    (e) the patients can return back to normal work relatively early with minimal loss of working days.
While in the corresponding open conventional surgeries a relatively large body part consisting of skin and muscle needs to be cut in order to gain access to an underlying body tissue cavity, in endoscopic surgery instead of cutting body structures like skin and muscle an endoscope is introduced into the body cavity via the natural opening of a cavity, if such exists, or alternatively a minute hole is made in the wall of the cavity through which the endoscope is introduced to visualize the interior of the body tissue cavity and to perform major or minor endoscopic surgical procedures. For this reason endoscopic surgery is also sometimes called ‘key hole’ or ‘minimal access surgery’. Besides reducing the pain associated with surgery, endoscopic surgery also helps in reducing the medical expenses.
Endoscopic Surgery is Primarily Related to a Tissue Cavity:
All endoscopic surgeries are carried out on a existing body cavity which is distended or ‘ballooned up’ by a suitable distending apparatus which permits the inner lining of the said tissue cavity to be visualized by the help of an endoscope. Though multiple endoscopic procedures have become established as the preferred surgical modality but still there is immense scope of increasing the safety and efficiency of the such existing endoscopic procedures by improving upon the existing techniques and apparatus used for distending body tissue cavities. Hysteroscopy, arthroscopy, TURP (transuretheral resection of the prostate), endoscopic surgery of the brain and endoscopic surgery of the spine are few of the routinely performed endoscopic procedures and the organs related to such surgeries being uterus, human joints, bladder, brain and the spine respectively. The list of endoscopic surgeries is long, ever increasing and there is hardly any body organ or organ system to which the benefits of endoscopy have not been extended.
Tissue Cavitiy is Initially Collapsed in its Natural State:
In the natural state tissue cavities are collapsed structures and the cavity walls are in apposition with each other as if kissing each other. Thus if an endoscope is introduced in such a collapsed cavity no endoscopic visualization is possible unless the cavity is ballooned up by filling it with a transparent fluid or a gas. Such ballooning of a tissue cavity is technically termed as ‘cavity distension’. No endoscopic procedure can be performed without an efficient cavity distending system and no endoscopic procedure should be attempted without a safe distending system because unsafe tissue cavity distending means can lead to extreme human morbidity and even the death of a patient and such grim realities shall be discussed in the later sections of this manuscript. Cavity distension provides both endoscopic visualization and mechanical distension which is necessary for the movement of endoscopic instruments.
Continuous Flow Irrigation:
In the present invention, the Inventors are focused on a system for distending body tissue cavities for those endoscopic procedures in which the cavity needs to be distended by utilizing continuous flow irrigation only. Here, the term ‘continuous flow irrigation’ means that fluid simultaneously enters and escapes from a tissue cavity via separate entry and exit points, as a result of which a positive fluid pressure is created inside the tissue cavity which distends the cavity.
The Need for Continuous Flow Irrigation:
Any tissue cavity can be easily distended in a ‘static manner’ by simply pushing fluid via a single inflow tube inserted into the cavity and in this manner a desired cavity pressure can be developed and also maintained. For example, a cavity can be distended by pressing on the piston of a simple syringe filled with fluid with the outlet end of the syringe being connected to the cavity by a tube. Alternatively a fluid filled bottle may be elevated to a suitable height and under the influence of gravity fluid from such bottle may be allowed to enter the cavity via a tube connecting the said bottle to the cavity and in this manner a desired static pressure can be developed and also maintained. Though it is very easy to achieve distension by the said static manner, it is not a practical solution because blood and tissue debris which are invariably released from the fragile cavity inner lining mix with the distending fluid and endoscopic vision gets clouded within a few seconds or a few minutes. Thus continuous flow irrigation is needed to constantly wash away blood and tissue debris in order to maintain constant clear endoscopic vision.
Cavity Pressure and Cavity Flow Rate:
It is obvious that cavity fluid pressure and the flow rate through the cavity are the two basic parameters associated with all continuous flow irrigation systems.
An Efficient Distending System:
The Inventors believe that an efficient distending system is the one which provides a predictably continuous clear visualization and a predictably stable mechanical stabilization of the cavity walls. In order to achieve this the Inventors believe that a suitable stable constant precise cavity pressure and a suitable stable precise cavity flow rate have to be created and maintained in a predictable and controlled manner. The cavity pressure should be adequate so that vision is not clouded by oozing of blood and enough mechanical separation of the cavity walls occurs to allow the movement of the endoscope. Similarly, the cavity flow rate should be adequate enough to constantly wash away blood and tissue debris in order to allow clear vision. Many prior systems utilize a peristaltic pump over the inflow and or the outflow side and these peristaltic pumps create pressure pulsations which are then transmitted to the tissue cavity. Such pressure pulsations are undesirable and the main aim of the present invention is to dampen such pressure pulsations.
A Safe Distending System:
An efficient distending system as explained in the previous paragraph need not also be a safe distending system. In this regard, the Inventors would like to highlight that if the cavity pressure rises above the prescribed safe limits excessive fluid intravasation may occur or the cavity may even burst. Fluid intravasation is a process by which the irrigation fluid enters into the patient's body system through the cavity walls and may cause significant danger to the patient's life including death. Thus a safe distending system is one which prevents or minimizes fluid intravasation and allows the surgeon to accurately know the instantaneous real time rate of fluid intravasation into the patient's body system.
No Prior Art is Absolutely Safe:
Many different types of uterine distending systems are known and are being commercially marketed by many different companies but none of these systems can be considered to be absolutely safe for the patient. This fact has been clearly stated in the ‘Hysteroscopic Fluid Monitoring Guidelines proposed by the Ad Hoc Committee on Hysteroscopic Fluid Guidelines of the American Association of Gynecologic Laproscopists February 2000 (Loffler F D, Bradley L D, Brill A I et al: Hysteroscopic fluid monitoring guidelines. The journal of the Americal Association of Gynecologic Laproscopists 7(1): 167-168, 1994) where the authors clearly and explicitly state “fluid pumps for low-viscosity media are a convenience and do not guarantee safety”. The present invention aims at providing a distending system which is both safer and more efficient in comparison to all the prior art systems.
Basic Physics of Cavity Distension:
Although, a person skilled in the art may know it, the Inventors would like to provide a brief description of the basic physics of cavity distension. Filling the tissue cavity with fluid enables distension of the same. Initially more fluid is pumped in than the amount which is extracted from the cavity and ultimately the inflow rate is fixed at a level where a somewhat desired cavity pressure and distension is achieved. It may be possible to accurately maintain the desired pressure and distension in the case of a rigid cavity, for example a cavity made of steel.
However, the body tissue cavities are not rigid because they are distensible and also have some element of elasticity. Thus a distended tissue cavity in its attempt to constantly revert back to its natural collapsed state reacts by exhibiting physiological contractions of the cavity wall which generally leads to variations in the cavity pressure which ultimately culminates in irregular movement excursions of the cavity walls. In a static system the said movement excursions may be so minute that they may even go unnoticed. However in a dynamic system such that being created during an endoscopic procedure, the said physiological cavity wall contractions may cause the cavity to expel out its entire fluid content thus leading to a surgically dangerous large magnitude movement excursion of the cavity wall. Because of these reasons it is extremely difficult to maintain the cavity pressure and cavity distension in a predictably stable fashion.
Further, the inflow tube, the out flow tube and the endoscope also invariably move and shake during surgery which leads to variations in fluid flow resistance which is also manifested in the form of variations in the cavity pressure. The cavity pressure variations occurring as a result of cavity wall contractions and the mechanical movement of the tubes and the endoscope tend to occur again even if they are corrected once because it is impossible to prevent the physiological cavity wall contractions and the mechanical movements of the irrigation circuit. Thus, the said cavity pressure variations shall continue to occur even after multiple repeated corrections.
Thus, till date the surgeon was only left with two options, either to ignore the said cavity pressure variations by not correcting them, or to externally and actively correct such pressure variations. The Inventors have noticed that any attempt to externally and actively correct the said cavity pressure variations leads to an undesirable turbulence inside the cavity and also tends to amplify the resultant movement excursions of the cavity walls. Thus there is a grave need to provide a system which can maintain an almost constant and stable cavity pressure even in the presence of the said physiological cavity contractions and the mechanical movements in the irrigation circuit.
Brief Description of an Endoscope
Prior to describing the basic layout of a continuous flow irrigation system the basic structure of an ‘endoscope’ needs to be described. Endoscope is a cylindrical tube having an outer diameter ranging between 3 to 9 mm approximately. A typical endoscope has four channels. One channel is meant to pass a fibereoptic telescope while endoscopic instruments are negotiated through a second instrument channel. A third channel also known as the inflow channel is used for pushing irrigation fluid into a tissue cavity, the proximal end of this channel ending in a metal adaptor known as the inflow port while the distal end of this inflow channel opens near the tip of the endoscope. The inflow port is connectable to an inflow tube which carries sterile irrigation fluid from a fluid source reservoir. A fourth channel also known as the out flow channel is meant for extracting waste fluid out of the cavity, the proximal end of this channel ending in a metal adaptor known as the outflow port while the distal end of this outflow channel opens near the tip of the endoscope. The outflow port is connectable with an outflow tube which transports the waste fluid from the cavity to a suitable waste fluid collecting reservoir. A set of fiber optic bundles contained inside the telescope transmit light energy produced by an external light source. This light energy illuminates the walls of the tissue cavity. The image thus formed is carried via a separate set of optical pathways again situated inside the telescope. A video camera attached to the eye piece of the telescope forms a clear endoscopic image of the cavity on a TV monitor. The endoscopic surgeon has to continuously look at the TV monitor all through the endoscopic procedure.
Basic Layout of a ‘Continuous Flow Irrigation System:
Henceforth in this manuscript unless otherwise specified the term ‘distension’ shall be deemed to imply tissue cavity distension by ‘continuous flow irrigation’ only and the term ‘cavity’ unless specifically stated shall be deemed to refer to a ‘body tissue cavity’. In a typical distension system a physiological non viscous liquid like 0.9% normal saline, 1.5% glycine, mannitol, ringer's lactate and 5% dextrose is stored in a sterile fluid source reservoir. A fluid supply tube connects the said fluid reservoir with the inlet end of a pump. The outlet end of the inflow pump is connected to the inflow port of an endoscope. When the inflow pump operates the fluid from the fluid source reservoir is sucked via the fluid supply tube and the inflow pump pushes this fluid into the tissue cavity via the said inflow tube. The pump operates by consuming certain amount of energy and as a result of this a positive fluid pressure is created inside the tissue cavity. An outflow tube extends between the outflow port and the inlet end of an outflow pump. When the outflow pump operates it actively extracts waste fluid from the cavity again at the expense of energy and this waste fluid is ultimately sent to a waste fluid reservoir via a tube which connects the outlet end of the outflow pump with the waste fluid reservoir. Alternatively the outflow pump may be missing and in such case the outflow tube directly carries the waste fluid from the cavity to the waste fluid reservoir and the energy for such act is supplied by gravity instead of the outflow pump. Also, the inflow pump may be missing and in such case the inflow tube directly supplies the irrigation fluid from a fluid source reservoir to the cavity. In such case the fluid source reservoir is hung at a suitable height above the patient and the said energy for cavity distension is derived from gravity instead of the inflow pump. A suitable pressure transducer is attached to the inflow tube, the outflow tube or directly to the cavity to measure the fluid pressure. A controller may be incorporated to regulate the system.
The Simplest Continuous Flow Irrigation System:
In its simplest form, a continuous flow irrigation system comprises a fluid reservoir bottle hung at a suitable height above the patient and an inflow tube connecting this fluid reservoir to a tissue cavity. An out flow tube is incorporated to remove fluid from the tissue cavity. In this system there is no pump and no transducer. In such a system fluid flows from the fluid source reservoir into the cavity and the required energy is supplied by gravity. The pressure developed inside the cavity can be increased or decreased by elevating or lowering the height of the fluid source reservoir. In such system the main limiting factor is the height of the room ceiling beyond which the fluid reservoir cannot be raised. This is a crude system having negligible practical importance and has been included only from the academic point of view. Also in such a system unlimited volume of irrigation fluid may enter into the patient's blood circulation. Thus such system is not suitable even from the patient safety point of view.
Basic Components of a Continuous Flow Irrigation System:
Like a motor car is made up of certain obvious components like engine, tyres and a steering wheel, a continuous flow distending system is made of components like pump, pressure transducer, flow regulating valve, rubber tubes and a controller. The pump may be a positive displacement pump like a peristaltic pump, piston pump or a gear pump or alternatively it may be a dynamic pump like a centrifugal pump. Further the said pump may be of a fixed RPM type which runs at fixed RPM all through the endoscopic procedure or the pump may be of a variable RPM type which operates at variable RPM during the endoscopic procedure. It is extremely important to note that fixed RPM pumps and variable RPM pumps are two separate mechanical entities in context with a cavity distending system because the fixed and variable RPM pumps impart different surgical efficiency and patient safety criteria to the distending system. The said pump may be attached on the inflow side only, on the outflow side only or both on the inflow and outflow side. Further if a pump is attached only on the inflow side the outflow tube may directly empty in a waste fluid reservoir at atmospheric pressure or a vacuum source may also be additionally attached. In some distending systems a flow controlling valve is attached on the outflow tube in order to regulate the cavity pressure. There may be a single pressure transducer attached to the inflow tube, the outflow tube or directly to the cavity. In some systems instead of one pressure transducer two pressure transducers may be used, one on the inflow tube and the other on the outflow tube.
Relvant references have been included in a PCT application filed by us in the past however three additional references are now being included. These references are U.S. Pat. No. 5,520,638, U.S. Pat. No. 4,902,277 and U.S. Pat. No. 5,578,012.
In U.S. Pat. No. 5,520,638 a variable speed peristaltic pump is used to push irrigation fluid into a tissue cavity. This patent is related to the ‘Continuous Wave II Arthroscopy Pump’ marketed by Arthrex. A chamber with volume is connected to the inflow tube and a collapsible bladder is contained within the bladder. The collapsible bladder has an open end connected with tubing to a pressure transducer. Once activated the pump begins to introduce fluid into the tissue cavity via the inflow tube and as pressure builds within the tissue cavity, fluid enters the chamber, and air in the chamber is compressed. The compressed air in the chamber compresses the bladder. Air pressure in the bladder is experienced by the pressure transducer. The pressure transducer feeds pressure information to a controller which regulates the RPM of the pump on the basis of a pressure feedback mechanism. Thus by the help of a pressure feedback mechanism the pressure inside a tissue cavity is maintained by fluctuating around a desired value. In this invention an important purpose of the said chamber is to dampen the pressure pulsations created by the peristaltic pump. Such pressure pulsations create turbulence inside the tissues cavity and are hence undesirable. The method of dampening the pressure pulsations as described in this U.S. Pat. No. 5,520,638 is not adequately efficient, especially at high pump RPM's. In the present invention a method shall be described by which the amplitude of the said pressure pulsations would be reduced to negligible magnitude even at a high pump RPM.
In U.S. Pat. No. 4,902,277 a pump is provided on the inflow side which pushes fluid into a tissue cavity while a positive displacement pump removes fluid from the cavity. This patent is related to ‘FMS duo Fluid Management System’ marketed by FMS Group. By the help of a pressure feedback mechanism the inflow pump is constantly increased or decreased thereby maintaining the cavity around a desired value. Thus by the help of a pressure feedback mechanism the pressure inside a tissue cavity is maintained by fluctuating around a desired value.
In U.S. Pat. No. 5,578,012 a centrifugal pump is deployed on the inflow side while no pump is deployed over the outflow side. This patent is related to the ‘HydroFlex HD’ pump marketed by DAVOL company. By the help of a pressure feedback mechanism the inflow pump is constantly increased or decreased thereby maintaining the cavity around a desired value. Thus by the help of a pressure feedback mechanism the pressure inside a tissue cavity is maintained by fluctuating around a desired value.